Many devices, such as protective passive restraints or air bags used in motor vehicles, escape slide chutes, life rafts, and the like, are normally stored in a deflated state and are inflated with gas substantially instantaneously at the time of need. Such devices are generally stored and used in close proximity to humans and, therefore, must be designed with a high safety factor which is effective under all conceivable ambient conditions.
Inflation is sometimes accomplished solely by means of a gas generative composition. At other times, inflation is accomplished by means of a gas, such as air, nitrogen, carbon dioxide, helium, and the like, which is stored under pressure and further pressurized and supplemented at the time of use by the addition of high temperature combustion gas products produced by the burning of a gas-generative composition.
It is, of course, critical that the gas-generative composition be capable of safe and reliable storage without decomposition or ignition at temperatures which are likely to be encountered in a motor vehicle or other storage environment. For example, temperatures as high as about 107.degree. C. (225.degree. F.) may reasonably be experienced. It is also important that substantially all the combustion products generated during use be non-toxic, non-corrosive, non-flammable, particularly where the inflator device is used in a closed environment, such as a passenger compartment of a motor vehicle.
Broadly, the present invention is directed toward gas generative compositions which exhibit low concentrations of insoluble combustion products. In this regard, the gas generative compositions of the present invention are embodied in a solid mixture of a nitrogen-containing fuel and an oxidizer selected from oxides of copper, nitrates of copper and strontium, and mixtures thereof. Most preferably, the nitrogen-containing fuel is azodicarbonamidine dinitrate (AZODN) and/or 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, colloquially known in the art as "CL-20". The oxidizer is most preferably copper (II) oxide (CuO) and/or basic copper nitrate (also known as copper trihydroxynitrate (Cu(NO.sub.3)hd 2.3Cu(OH.sub.2) and/or strontium nitrate (Sr(NO.sub.3).sub.2).
It has been discovered that the compositions of the present invention provide high burning rates with acceptable burning rate pressure exponents which allow their operation at lower pressures, thereby resulting in the use of less costly, lower weight, and lower strength materials for design and manufacture of the inflator pressure vessel. In accordance with this invention, the use of nitrate and perchlorate salts of azodicarbonamidine, and in particular azodicarbonamidine dinitrate, or hexanitrohexaazaisowurtzitane (CL-20) and mixtures thereof, in combination with oxidizers such as copper oxide, basic copper nitrate, strontium nitrate or mixtures thereof, and optionally a binder for providing structural integrity, results in heterogeneous propellant compositions which provide greater total gas output and a lower concentration of insoluble solid combustion products, than when such oxidizers are used with prior art fuels such as guanidine nitrate, aminoguanidine nitrate, nitroguanidine, ethylenediamine dinitrate, cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), and various tetrazole derivatives, such as 5-aminotetrazole, diammonium bitetrazole, and potassium 5-aminotetrazole.
As discussed above and in accordance with the present invention, a distinct advantage results from the use of azodicarbonamidine dinitrate (AZODN) and/or hexanitrohexaazaisowurtzitane (CL-20) as the major fuel component because the nitric acid salt of azodicarbonamidine, and CL-20, have a significantly better oxygen balance as compared to conventional fuels. This improved oxygen balance thereby allows the use of a significantly lower concentration of oxidizer to maintain the proper stoichiometry for burning to substantially innocuous gaseous combustion products consisting of carbon dioxide, nitrogen, and water vapor. In addition, because a lower concentration of solid oxidizer is required, an associated lower concentration of substantially insoluble and clinkerable solid combustion products are formed when compared with prior art formulations. Because a lower total concentration of solid combustion products is formed, acceptable filtration of the solid products which do not clink and are not trapped in the combustion chamber is readily achieved by using fewer mechanical screens or other filtering media within the inflator, and still retain a lowered susceptibility for initiating an asthmatic reaction from the occupant of the vehicle.
The gas generant compositions of this invention are particularly useful when employed in inflatable passive vehicle occupant restraint systems (e.g., air bag systems). Thus, the compositions of this invention may be employed as a monopropellant, fuel or partial fuel ingredient for use in hybrid inflation systems, airbag propellants, multiple airbag propellant combinations, ignition mixtures, and auto ignition pill (AIP) compositions.
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.